1. Field of the Invention
The present invention relates to a conductive paste composition for an internal electrode, which is effective for controlling shrinkage, a multilayer ceramic capacitor having improved electrical characteristics, and a fabrication method thereof.
2. Description of the Related Art
Recently, as electronic products have been reduced in size, a multilayer ceramic electronic component has also required to be reduced in size, yet have a large capacity.
Thus, dielectric layers and internal electrodes have been attempted to be thinned and multi-layered according to various methods, and recently, multilayer ceramic electronic components having thinned dielectric layers while having a larger number of laminations have been fabricated.
Also, in order to thin internal electrodes, ceramic electronic components including inner electrodes formed by using a fine metal powder have been fabricated.
In particular, multilayer ceramic capacitors are fabricated by laminating hundreds of inner electrodes and dielectric layers or more.
In a fabrication process of a multilayer ceramic capacitor, a firing process is required to thermally heat a laminate to a temperature of up to 1200° C. in order to implement capacitor characteristics (in particular dielectric layers).
Here, internal electrode layers made of a metal may be greatly changed and deformed in volume due to a firing process, in comparison to dielectric layers made of a ceramic material.
In order to fabricate a multilayer ceramic capacitor having excellent electrical characteristics, it is necessary to control deformation of internal electrode layers. To this end, a technique of adding a base substance (or a sintering inhibitor, i.e., a ceramic material for delaying nickel powder shrinkage) to a conductive paste composition for an internal electrode, a technique of oxidation-coating nickel powder, or the like has been introduced.
Meanwhile, during a process of fabricating a multilayer ceramic capacitor, internal electrodes are required to undergo a debinder calcining process. Here, pure nickel particles are easily oxidized and expanded in volume, and strain acts on the internal electrodes during the process to potentially cause so-called oxidation cracks and result in a broken chip. Thus, in order to prevent oxidation cracks and to widen a process window, a method of using nickel particles coated with a nickel oxide has been introduced.
However, in the process of fabricating a multilayer ceramic capacitor using nickel particles coated with a nickel oxide, a high temperature reduction atmosphere thermal treatment for firing dielectrics is inevitably performed, even on the internal electrodes, and thus, shrinkage behavior of internal electrodes greatly affects electrical characteristics of the multilayer ceramic capacitor.
Namely, the internal electrodes (nickel) are reduced in volume and agglomerate during the foregoing process. This directly affects electrode connectivity and electrode coverage of the multilayer ceramic capacitor.
Also, during the reduction atmosphere thermal treatment, a nickel oxide constituting a coating layer of nickel is reduced to a nickel metal.
In general, a density of a nickel oxide is 6.67 g/cm3 and that of a nickel metal is generally 8.90 g/cm3.
Thus, as a nickel oxide layer is reduced to a nickel metal during reduction atmosphere firing, about 41% (over the content of a nickel oxide) of shrinkage occurs in addition to the shrinkage resulting from a sintering behavior.
In order to control sintering shrinkage of nickel particles, a base substance (or a sintering inhibitor, i.e., a ceramic material for delaying shrinkage of nickel powder) may be used. However, currently, there is no appropriate method of controlling shrinkage according to nickel oxide reduction.
In particular, as nickel particles are grain-refined, the volume parts of the nickel oxide in nickel particles are increasing, so the necessity of controlling shrinkage of conductive paste for an internal electrode is further increasing.